Can nanoscale surface charge heterogeneity really explain colloid detachment from primary minima upon reduction of solution ionic strength?

This study theoretically examined colloid detachment from primary minima with ionic strength (IS) reduction on heterogeneous collector surfaces. The chemically and physically heterogeneous collector surfaces were modeled as a planar surface carrying nanoscale patches of different zeta potentials and nanoscale pillars/hemispheroids, respectively. The surface element integration technique was used to calculate interaction energies between colloid and collector surfaces. Two boundary conditions for the double-layer interaction energy were considered, namely constant surface potential (CSP), and linear superposition approximation (LSA). In contrast to prevailing opinions in the literature, our results show that colloids attached on the chemically heterogeneous surface cannot be detached by IS reduction under CSP condition due to an increase of the adhesive force/torque with decreasing IS. Detachment from chemically heterogeneous surfaces by IS reduction can occur under LSA condition only when the flow velocity is very high. In contrast, the presence of nanoscale physical heterogeneity can cause colloid detachment from primary minima by IS reduction under both CSP and LSA conditions at flow velocities commonly used in experimental studies because of a significant reduction in the adhesive forces/torques.     

Observation of bistability in a CO2 laser exhibiting passive Q-switching

Optical bistability has been investigated experimentally in a CO₂ laser containing CF₃Br as a saturable absorber. The frequency dependence of the hysteresis cycle of this laser containing a saturable absorber (LSA) has been studied. It has also been shown that the LSA may undergo simultaneously hysteresis cycles and Q-switching. The phase diagram of the LSA has been extended towards regions where this behavior has been observed.     

Microstructure, microhardness, composition, and corrosive properties of stainless steel 304 I. Laser surface alloying with silicon by beam-oscillating method.

Laser surface alloying (LSA) with silicon was conducted on austenitic stainless steel 304. Silicon slurry composed of silicon particle of 5 μm in average diameter was made and a uniform layer was supplied on the substrate stainless steel. The surface was melted with beam-oscillated carbon dioxide laser and then LSA layers of 0.4–1.2 mm in thickness were obtained. When an impinged energy density was adjusted to be equal to or lower than 100 W mm⁻², LSA layers retained rapidly solidified microstructure with dispersed cracks. In these samples, Fe₃Si was detected and the concentration of Si in LSA layer was estimated to be 10.5 wt.% maximum. When the energy density was equal to or greater than 147 W mm⁻², cellular grained structure with no crack was formed. No iron silicate was observed and alpha iron content in LSA layers increased. Si concentration within LSA layers was estimated to be 5 to 9 wt.% on average. Crack-free as-deposited samples exhibited no distinct corrosion resistance. The segregation of Si was confirmed along the grain boundaries and inside the grains. The microstructure of these samples changed with solution-annealing and the corrosion resistance was fairly improved with the time period of solution-annealing. Received: 2 September 1999 / Accepted: 6 September 1999 / Published online: 1 March 2000     

Effect of temperature on the sliding wear behavior of laser surface alloyed Ni-base on Al-Mg-Si alloy

The surface microstructures of 6061 Al-Mg-Si alloy coated with laser surface alloyed (LSA) Ni-Cr-B-Si powder and their sliding wear performance have been investigated. Experimental results show that there are three regions, as grayish region (G.R.), dark region (D.R.) and bright region (B.R.), in the pool. The Al₃Ni and Al₃Ni₂ compounds appear in the G.R. and D.R., respectively. The Al-Ni-Cr amorphous structure can be observed in the B.R. The hardness of the LSA specimens is much higher than the Al-matrix. Compared with the Al-matrix, the LSA specimens have excellent sliding wear performance. They have lower friction coefficient and wear rate. The critical temperature of sliding wear resistance of LSA specimen is higher than that of Al-matrix by about 50 °C. The stress relief during thermal treatment will slightly reduce the hardness and the wear resistance of LSA specimens, especially at testing temperature >200 °C.     

不同退火方式对Ni/SiC接触界面性质的影响

采用快速热退火(rapid thermal annealing, RTA)法和脉冲激光辐照退火(laser spark annealing, LSA)法, 在n型4H-SiC的Si面制备出Ni电极欧姆接触. 经传输线法测得RTA样品与LSA样品的比接触电阻分别为5.2×10^-4 Ω·cm², 1.8× 10^-4 Ω·cm². 使用扫描电子显微镜、原子力显微镜、透射电子显微镜、拉曼光谱等表征手段, 比较了两种退火方式对电极表面形貌、电极/衬底截面形貌和元素成分分布、SiC衬底近表层碳团簇微结构的影响. 结果表明, 相比于RTA, LSA法制备出的欧姆接触在电极表面形貌、界面形貌、电极层组分均匀性等方面都具有明显优势, 有望使LSA成为一种非常有潜力的制备欧姆接触的退火处理方法.     

Microstructure and wear resistance of composite layers on a ductile iron with multicarbide by laser surface alloying

Multicarbide reinforced metal matrix composite (MMC) layers on a ductile iron (QT600-3) were fabricated by laser surface alloying (LSA) using two types of laser: a 5 kW continuous wave (CW) CO₂ laser and a 400 W pulsed Nd:YAG laser, respectively. The research indicated that LSA of the ductile iron with multicarbide reinforced MMC layers demonstrates sound alloying layers free of cracks and porosities. The microstructure, phase structure and wear properties of MMC layers were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), as well as dry sliding wear testing. The microstructure of the alloyed layer is composed of pre-eutectic austenite, ledeburite, spherical TiC, Cr₇C₃ and Cr₂₃C₆ with various morphologies. TiC particles are dispersed uniformly in the upper region of MMC layers. The average hardness of LSA layers by CO₂ laser and pulsed Nd:YAG laser is 859 HV_0.2 and 727 HV_0.2, respectively. The dry sliding wear testing shows the wear resistance of ductile iron is significantly improved after LSA with multicarbide.     

Optical bistability in gaussian inhomogeneously broadened ring lasers with saturable absorber

The optical bistability (OB) in Gaussian inhomogeneously broadened ring lasers with saturable absorber (LSA) in both resonance and out-of-resonance is theoretically analyzed in the rate-equation approximation based on the dual two-level model. The OB effect may appear for appropriate sets of LSA control parameter values which can be displayed in phase diagrams. The characteristics of the OB curves as well as their stability behavior are analytically and numerically studied in detail. The influence of the control parameters, including detuning, are investigated and displayed in the figures. A brief comparison with the Lorentzian case is given as well. Paper submitted by authors in English April 20, 1999.     

Counterpropagating pattern dynamics: From narrow to broad beams

The development of patterns in counterpropagating (CP) beams in saturable Kerr-like media is investigated in a numerical study, by varying the width of beams. A model of interacting mutually incoherent beams is adopted, with slow local changes in the index of refraction, and a numerical simulation of propagating beams is performed for different values of the driving parameters. Linear stability analysis (LSA) of CP beams is carried out, and a modulational instability threshold for the appearance of side beams is determined. The results of LSA, concerning the instability of plane waves, are compared with the numerical results concerning broad hyper-Gaussian beams whose width is varied. Qualitative agreement is found, due to the similarity between plane waves and flat-top hyper-Gaussian beam profiles. Owing to very slow quasi-steady-state changes in the system during time evolution, the transverse characteristics of beam distributions, determined by LSA, are found to persist for long in the transient evolution of CP beams.     

Parameterization of land surface albedo

Remote measurements of Earth’s surface from ground, airborne, and spaceborne instruments show that its albedo is highly variable and is sensitive to solar zenith angle（SZA） and atmospheric opacity. Using a validated radiative transfer calculating toolbox, DISORT and a bidirectional reflectance distribution function library, AMBRALS, a land surface albedo（LSA） lookup table（LUT） is produced with respect to SZA and aerosol optical depth. With the LUT, spectral and broadband LSA can be obtained at any given illumination geometries and atmospheric conditions. It provides a fast and accurate way to simulate surface reflectance over large temporal and spatial scales for climate study.     

Optical bistable behavior of single-mode fabry-perot lasers with saturable absorber

The present paper is devoted to the optical bistable behavior of Gaussian inhomogeneously broadened single-mode Fabry-Perot lasers with saturable absorber (LSA) in both resonance and nonresonance. The system is described by rate equations based on the dual two-level model with allowance for spontaneous emission and spatial hole-burning. The conditions under which optical bistability (OB) occurs are clearly displayed in phase diagrams. The OB characteristics and stability behavior are investigated in connection with their dependence on the detuning and LSA parameters. Paper submitted by authors in English April 20, 1999.     

Process monitoring of powder pre-paste laser surface alloying

Instead of the continuous powder delivery method using a powder feeder for thick layer laser cladding, pre-pasting of the alloying powder on the substrate is a widely used method to supply the coating powders into the melt pool for LSA. A method to monitor the process of laser surface alloying based on the infrared emission from the melt pool using infrared photodiodes was developed. The technique is solely aimed at the process of laser surface alloying using pre-paste metal powder on the substrate surface prior to laser melting. This monitoring technique is able to distinguish the existence or the absence of the pre-paste powder and the consistency of the laser surface alloying process. The technique is of low cost and is simple to implement into the process.     

Measurement and Analysis of Composition and Depth Profile of H in Amorphous Si1-xCx:H Films

Composition in amorphous Si1-xCx：H heteroepitaxial thin films on Si （100） by plasma enhanced chemical vapour deposition （PECVD） is analysed. The unknown x （0.45-3.57） and the depth profile of hydrogen in the thin films are characterized by Rutherford backscattering spectrum （RBS）, resonance-nuclear reaction analysis （R-NRA） and elastic recoil detection （ERD）, respectively. In addition, the depth profile of hydrogen in the unannealed thin films is compared to that of the annealed thin films with rapid thermal annealing （RTA） or laser spike annealing （LSA） in nitrogen atmosphere. The results indicate that the stoichiometric amorphous SiC can be produced by PECVD when the ratio of CH4/SiH4 is approximately equal to 25. The content of hydrogen decreases suddenly from 35% to 1% after 1150℃ annealing. RTA can reduce hydrogen in SiC films effectively than LSA.     

Preparation and luminescence characterization of fine-sized LaSr2AlO5:Ce phosphor prepared by spray pyrolysis

Fine-sized (La_1−x,Ce_x)Sr₂AlO₅ (LSA:Ce) yellow phosphor particles were prepared by spray pyrolysis. The crystal structure and optical properties of prepared LSA:Ce particles were studied by changing the reduction temperature and the Ce content. The LSA:Ce particles had spherical-like shape and fine size of less than ∼2 μm in the reduction temperature range from 1300 to 1450 °C. The luminescence intensity was steadily improved by elevating the reduction temperature due to the increase of crystallinity. A redshift in the emission peak was observed on increasing the Ce content due to the reduction of Ce-O distance. Concentration quenching in the luminescence intensity was observed when the Ce concentration was 1% (x=0.01), which was caused mainly by the electric dipole-dipole interaction. The critical transfer distance was calculated as 29 Å, which is in good agreement with the value estimated from the spectral data.     

基于LSA与PCA的常见滋补中药NIR聚类

潜在语义分析在信息检索领域应用较多,但在近红外光谱领域应用较少.利用近红外漫反射光谱技术,结合潜在语义分析（LSA）和主成分分析（PCA）,比较了不同预处理方法、不同奇异值和主成分个数对所建模型的影响,最后确定的模型校正集误判数分别为4和3.用建立的校正模型对验证集进行验证,总的识别率分别达到了96.00％和96.50％.对于功效较近、难以聚类的滋补中药,潜在语义分析是一种新的有效的方法.     

Stability of a charged drop near a conductor wall

The effect of conductor boundaries on the deformation and stability of a charged drop is presented. The motivation for such a study is the occurrence of a charged conductor drop near a conductor wall in experiments (Millikan-like set-up in studies on Rayleigh break-up) and applications (such as electrospraying, ink-jet printing and ion mass spectroscopy). In the present work, analytical (linear stability analysis (LSA)) and numerical methods (boundary element method (BEM)) are used to understand the instability. Two kinds of boundaries are studied: a spherical, conducting, grounded enclosure (similar to a spherical capacitor) and a planar conducting wall. The LSA of a charged drop placed at the center of a spherical cavity shows that the Rayleigh critical charge (corresponding to the most unstable l = 2 Legendre mode) is reduced as the non-dimensional distance ?d = (b - a)/a decreases, where a and b are the radii of the drop and spherical cavity, respectively. The critical charge is independent of the assumptions of constant charge or constant potential conditions. The trans-critical bifurcation diagram, constructed using BEM, shows that the prolate shapes are subcritically unstable over a much wider range of charge as [Formula: see text] decreases. The study is then extended to the stability of a charged conductor drop near a flat conductor wall. Analytical theory for this case is difficult and the stability as well as the bifurcation diagram are constructed using BEM. Moreover, the induced charges in the conductor wall lead to attraction of the drop to the wall, thereby making it difficult to conduct a systematic analysis. The drop is therefore assumed to be held at its position by an external force such as the electric field. The case when the applied field is much smaller than the field due to inherent charge on the drop ((a(3)ρg)/(3ε(0)Ψ(2)) ? 1 is considered. The wall breaks the fore-aft symmetry in the problem, and equilibrium, predominantly prolate shapes corresponding to the legendre mode, l = 2 , are observed. The deformation increases with increasing charge on the drop. The breakup of the prolate equilibrium shapes is independent of the legendre modes of the initial perturbations. The prolate perturbations are subcritically unstable. Since the equilibrium prolate shapes cannot continuously exchange instability with equilibrium oblate shapes, an imperfect transcritical bifurcation is observed. A variety of highly deformed equilibrium oblate shapes are predicted by the BEM calculations.     

Laser spectral analysis of starch products

We have developed laser spectral analysis (LSA) methods for quality control of starch products in the raw material stage and after thermomechanical processing (extrusion). We show that it is possible to plot a common calibration curve for analyte elements in different types of analyte samples, i.e., we have established that there is no matrix effect on the analysis results.     

Analysis of the linear stability of stationary solutions in a circular laser containing a saturable absorber “LSA” for inhomogeneous broadening

In this present paper, the optical bistability in a circular laser containing a saturable absorber LSA for inhomogeneous broadening is studied. A simple mathematical model was developed to describe the action of this type of laser in a circular resonator under two conditions, when the spontaneous emission is neglected or included in the cavity. For both of these two cases, the coefficient of saturation was considered to be equal or different to unity (ζ=1 or ζ≠1). The photons intensities Q_j were determined as function of the pumping rate σ₀ of the active medium and analyzed the linear stability of the stationary solutions obtained in a circular laser containing a saturable absorber “LSA” for inhomogeneous broadening.     

Low-frequency noise of an LSA generator

A model of the low-frequency fluctuations of the oscillations of an LSA generator produced by accumulation and distribution of space-charge perturbations which occur at local micrononuniformities in the structure of the working region of a Gunn diode is proposed. Flicker fluctuations of the parameters of the nonuniformities are regarded as the primary source of noise. Expressions are obtained for the power spectra of the amplitude-frequency noise of the output signal. The dependence of the noise level on the bias field applied to the diode is analyzed and numerical estimates are given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 27, No. 1, pp. 79–86, January, 1984.     

Three-dimensional numerical simulations of cellular jet diffusion flames

Recent experimental investigations have demonstrated that the appearance of particular cellular states in circular non-premixed jet flames significantly depends on a number of parameters, including the initial mixture strength, reactant Lewis numbers, and proximity to the extinction limit (Damköhler number). For CO₂-diluted H₂/O₂ jet diffusion flames, these studies have shown that a variety of different cellular patterns or states can form. For given fuel and oxidizer compositions, several preferred states were found to co-exist, and the particular state realized was determined by the initial conditions. To elucidate the dynamics of cellular instabilities, circular non-premixed jet flames are modeled with a combination of three-dimensional numerical simulation and linear stability analysis (LSA). In both formulations, chemistry is described by a single-step, finite-rate reaction, and different reactant Lewis numbers and molecular weights are specified. The three-dimensional numerical simulations show that different cellular flames can be obtained close to extinction and that different states co-exist for the same parameter values. Similar to the experiments, the behavior of the cell structures is sensitive to (numerical) noise. During the transient blow-off process, the flame undergoes transitions to structures with different number of cells, while the flame edge close to the nozzle oscillates in the streamwise direction. For conditions similar to the experiments discussed, the LSA results reveal various cellular instabilities, typically with azimuthal wavenumber m = 1–6. Consistent with previous theoretical work, the propensity for the cellular instabilities is shown to increase with decreasing reactant Lewis number and Damköhler number.     

Optical Solitons and Stability Analysis in Ring-Cavity Fiber System with Carbon Nanotube as Saturable Absorber

This paper addresses the ring-cavity fiber laser system. A class of gray and black soliton solutions of the model are reported by adopting an appropriate envelope ansatz. Further more, the modulation instability (MI) of the equation is studied using the linear-stability analysis (LSA) technique and the MI gain spectrum is derived. Some physical interpretations and analysis of the results obtained are also presented.